(1) Field of the Invention
The present invention relates to pneumatic radial tires for two-wheeled vehicles, and particularly to a belt structure therefor. The invention is specifically aimed at increasing tread-gripping forces in the case that the vehicle turns, reducing the number of working steps in the formation of the belt, and decreasing the weight of the tire.
(2) Related Art Statement
Conventional pneumatic radial tires for two-wheeled vehicles have been heretofore known, in which a belt is provided on a radially outer peripheral side of a crown portion of a carcass by forming one belt ply through spirally winding one cord or a unit of plural cords around the crown portion of the carcass in parallel to the tire equatorial plane. It is confirmed that such tires can afford high speed durability and high speed stability.
However, the tire of this type has low bending rigidity in a widthwise sectional plane. Accordingly, particularly when a vehicle is turned under application of a camber angle to the tire, rigidity is insufficient in a shoulder portion of a tread, and therefore high tread-gripping forces cannot be unfavorably obtained. This defect is more serious with the increase in the turning speed.
Under the circumstances, as disclosed in Japanese patent application Laid-open No. 3-74,205, a technique has been proposed, in which bending rigidity is increased within a widthwise sectional plane of the tire by extending cords in a radially innermost cord ply in an angle of 40.degree. to 90.degree. with respect to an equatorial plane of the tire and extending cords in a cord ply adjacent radially outwardly to the radially innermost cord ply also in parallel to the tire equatorial plane, while spirally extending the cords of the radially outward cord ply in a width direction of the tire.
However, the proposed technique needs an additional step to bond the innermost cord ply on forming the tire, which unfavorably increase the number of working steps and the weight of the tire.